[krzyk]

> if you need to use a particular app, you can only get it from a third-party store that you don't trust

This sounds like iPhone user argument. In Android world you can have multiple app stores, but if you want your app to be used you must be on Google one, because it has the most eyes. Facebook didn't create their own app store.

Custom App stores are fringe apps, with exceptions of f-droid which is source of open source apps and many prefer it to google play (and apps are frequently on both stores) and maybe samsung/amazon ones because they are preinstalled on some devices.